Engines operating with a variable number of active or deactivated cylinders may be used to increase fuel economy, while optionally maintaining the overall exhaust mixture air-fuel ratio about stoichiometry. In some examples, half of an engine's cylinders may be disabled during selected conditions, where the selected conditions can be defined by parameters such as a speed/load window, as well as various other operating conditions including vehicle speed. A VDE control system may disable selected cylinders through the control of a plurality of cylinder valve deactivators that affect the operation of the cylinder's intake and exhaust valves.
Various approaches have been identified for diagnosing degradation in VDE operation, such as based on crankshaft vibrations related to engine firing order, firing frequency, etc. However, the inventors herein have recognized a disadvantage with such approaches. As an example, such approaches may be unable to identify particular situations, such as when one cylinder valve of a cylinder is properly deactivated, but another valve in the same cylinder continues to operate even when it is commanded to be deactivated.
Thus, in one example, the above issue may be addressed by a method of monitoring cylinder valve deactivation of a cylinder valve of an engine, the method comprising indicating degradation of cylinder valve deactivation in response to manifold pressure at or around a characteristic frequency.
In one example situation, a cylinder is commanded to be deactivated, and while an exhaust valve is properly deactivated, an intake valve continues to open during the intake stroke. Herein, the operation of the intake valve will cause intake air to be drawn into the cylinder and compressed. However, as the exhaust valve remains closed, the gasses in the cylinder will be expanded and then re-compressed during the exhaust stroke. As such, when the intake valve opens again at or near the next intake stroke, the compressed gas in the cylinder may be rapidly released and expanded in to the intake manifold. This rapid expansion may excite the resonance frequency of the air in the intake manifold, thereby creating pressure oscillations, vibrations, and noise, which may be compared to the striking of a bell. By monitoring the manifold pressure response at or around a characteristic frequency, such as the resonant acoustic frequency of air in the intake manifold, during selected conditions, such as the intake stroke or intake valve lift event of a cylinder, valve deactivation degradation may be identified.
In another example situation, a cylinder is commanded to be activated and while the intake valve is properly activated, an exhaust valve continues to remain closed during the exhaust stroke, or opens with a delay. Herein, as in the previous example situation, the gasses in the cylinder will be expanded and then re-compressed during the exhaust stroke. When the intake valve opens again at or near the next intake stroke, the compressed gas in the cylinder may be rapidly released and expanded in to the intake manifold, creating pressure oscillations, vibrations, and noise. Herein, as in the previous example, degradation of cylinder valve activation may be indicated in response to manifold pressure at or around a characteristic frequency, such as the resonant acoustic frequency of air in the intake manifold, during selected conditions, such as the intake stroke or intake valve lift event of a cylinder.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.